Optical media players and recorders, such as current compact disc (CD) and digital video disc (DVD) systems operate generally by directing an optical beam from a source, causing the beam to contact a specific location on an optical medium where data is stored, and receiving the data via the reflection of the beam back to receiving devices. To make this happen, current systems are required, at least, to perform two necessary functions, which are tracking and focusing.
Current focusing involves fine-tuning the manner in which the optical beam impinges upon the optical medium. Current tracking involves placing the beam (and consequently the source of the beam) in a specific location so it will impinge upon the optical medium in the appropriate place. Thus, in a current optical media player and/or recorder, the optical media typically is rotated and an optical beam is continually both focused onto the media and moved (using tracking functionality) to the appropriate place on the media, so that the data can be reflected back to a receiving device and output, for instance to a speaker and/or a television.
Therefore, a current optical media player operates generally as shown in FIG. 1 in order to allow a user to listen to a song, watch a movie or otherwise interact with data upon the medium. The player holds an optical medium 110, such as a CD or DVD. The medium 110 is caused to spin, and a light source 120 directs an optical beam 130 to the medium 110. The beam 130 then reflects back to a receiving device 140, via a reflector 115, where a focusing function 150 and a tracking function 160 work in tandem to make beam 130 both in the right place and converged to a point at the correct depth. As time passes (through a combination of spinning the medium 110 and the tracking function 160), the beam 130 may be directed across the entire spiral track 170 so that the entire CD or DVD can be accessed. Similarly, the beam 130 can be moved between tracks, for instance track A 180 and track B 190, when the user jumps between scenes and/or songs.
FIG. 2 provides an example of current focusing, which includes a more detailed analysis of focusing function 150 of FIG. 1. Focus is detected by focusing function 200, which comprises photocells A, B, C, and D in a conventional three beam tracking configuration where photocells A+C are compared to photocells B+D to obtain a focus error signal (FE) 210 from the reflection of beam 240 from medium 260 via reflector 265. FE is used in a feedback loop to connect to a beam source 220, typically an optical head, which is adjusted based on the results of A+C compared to B+D. Therefore the readings at A, B, C, and D are continually used to adjust the beam source 220 to maintain continual focus.
Currently any phenomenon that caused focus to differ between axial and radial dimensions would force a compromise between two optimum focal planes in the focusing function 200, one for each of the two dimensions. This results in a spot 250 on the medium 260 that is not as small and bright as would be possible if focusing function 200 was performed in a manner that more closely resembled a theoretically optimal focus.
Moreover, when using modern optical devices, such as those described with respect to a co-pending patent application entitled “Low Seek Time Optical Disc Tracking System”, filed on Dec. 22, 2004, and having application Ser. No. 10/905,231, (the disclosure of which is herein incorporated by reference) there is an improvement to the invention when each dimension of focus is independently adjustable, (even if resolved by interdependent means).